[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 190242
TCDAT5

Hurricane Nigel Discussion Number  15
NWS National Hurricane Center Miami FL       AL152023
1100 PM AST Mon Sep 18 2023

Nigel has become a little better organized this evening, with a
ragged eye becoming more apparent in infrared satellite imagery. An
earlier SSMIS microwave overpass revealed a fairly well-defined
low-level inner-core structure, but the eye was open to the
northwest. Subjective Dvorak intensity estimates from TAFB and SAB
were a consensus T4.5 (77 kt), and the various objective estimates
were in the 70-80 kt range at 0000 UTC.  Based on a blend of these
intensity estimates, the initial wind speed is set at 75 kt for
this advisory.

Although Nigel's strengthening appears to have been disrupted by
dry air entrainment today, the hurricane has about another 24-36
hours within low shear conditions and over warm SSTs in which
to strengthen. The NHC intensity forecast calls for additional
strengthening during that time, but the peak intensity has been
lowered slightly.  After 36-48 hours, increasing southwesterly
vertical wind shear and cooler SSTS along the track of Nigel are
expected to cause gradual weakening.  The NHC wind speed forecast
is in best agreement with the HFIP corrected-consensus aid, which
is at the higher end of the guidance in the short term.  The global
models indicate that extratropical transition is likely to begin by
72 hours, and that process should be complete by day 4.

Nigel continues to move northwestward (310 degrees) at about 10 kt.
The hurricane should continue on that general heading and speed
through midday Tuesday, but as it nears the western extent of the
ridge, Nigel is predicted to turn northwestward and northward
shortly thereafter.  By 48 hours, an approaching mid- to upper-level
trough is forecast to cause Nigel to accelerate northeastward over
the central and northeastern Atlantic through the remainder of the
forecast period.  The track guidance remains tightly clustered, with
the primary differences being how much Nigel accelerates
northeastward later in the period.  The NHC track forecast is a
blend of the typically reliable GFS and ECMWF models, nd is close
to the various consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT  19/0300Z 28.6N  52.7W   75 KT  85 MPH
 12H  19/1200Z 29.9N  53.8W   85 KT 100 MPH
 24H  20/0000Z 32.1N  54.5W   90 KT 105 MPH
 36H  20/1200Z 34.7N  54.1W   90 KT 105 MPH
 48H  21/0000Z 37.6N  51.6W   85 KT 100 MPH
 60H  21/1200Z 40.5N  46.6W   80 KT  90 MPH
 72H  22/0000Z 43.4N  39.5W   70 KT  80 MPH
 96H  23/0000Z 50.0N  24.7W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  24/0000Z 57.0N  17.4W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Brown
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